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Sph 2172: Physics Question Paper

Sph 2172: Physics

Course:Bachelor Of Science In Computer Science

Institution: Dedan Kimathi University Of Technology question papers

Exam Year:2010

Second Semester Examinations 2009/2010
SUPPLEMENTARY
First Year Examinations for the Degree of Bachelor of Science in Computer Science
SPH 2172: Physics
Date: Time:2 Hours
Instructions: Answer the first equation and any two other questions
1. (a) State in words Coulomb’s law. Write it down analytically in a way that reflects all the aspects of interaction of electric charges. Give the name and SI units of all symbols used.
(5 marks)
(b) Define correctly “capacitance”. Give the name of its SI units. Express it in base SI units.
(5 marks)
(c) State exactly the Ohm’s law. From there, define “Resistance”. Give the name of its SI unit. Express that unit through basic SI units (5 marks)
(d) Write down the law of interaction of two straight conductors, often referred to as “Ampere’s law” and from there, define the Ampere as one of base units of SI system of units. (5 marks)
(e) State correctly the Faraday’s law of electromagnetic induction. Write it down Give the name and SI units of all symbols used. (5 marks)
(f) What is a diode? Give and comment its V-I characteristics curve. What is its main application in electronics? (5 marks)
2. (a) What is meant by the “electric field” (sometimes called electric field intensity or electric field strength) at a point of space. What it its SI unit. Express it in base SI units
(5 marks)
(b) A copper sphere of massm ? 2.g contains about 22 N ? 2X10 atoms. The charge on the
nucleus of each atom is q ? 29e . What fraction of the electrons must be removed from the
sphere to give it a charge of Q ? 2?C ? (6 marks)
(c) A three-way light bulb has two filaments which are connected to three wires as shown in
Fig. 1. By turning the socket switch, 120 V is put across either ab, bc, or ac.
Fig.1. For question 1(c)
(i) If ?144? 1 R and ? 216? 2 R , what are the three possible power dissipation of the
light bulb?
(ii) A different three-way light bulb can operate at 300, 100and 75W . What are the
resistances of its two filaments? (9 marks)
3. (a) Define “ electric potential” at a point of space. What is its SI unit? Express that unit
through base SI units (6 marks)
(b) Determine the absolute potential in air at a distance of d ? 3cmfrom a point charge of
Q ? 50nC (7 marks)
(c) A bulb rated 120V /90W is operated from a 120 ?V voltage source. Find the current
flowing through it and its resistance (7 marks)
4. (a) Define” electric current” and “electric current density”. What are the SI of these
quantities (6 marks)
(b) The electron beam in a TV tube consists of electrons accelerated from rest through a
potential difference of about 20kV . How large an energy does the electron have? What is
its speed? We ignore relativistic effects.m X kg e
31 ? 9.1 10 (6 marks)
(c) We can measure resistance using an ammeter jointly with a voltmeter. This is called
“volt-ampere” method. Draw the schematic diagram of such a circuit taking in account
the internal resistance of the ammeter A R and that of the voltmeter V R and show how
mathematically the value of R is determined from the readings of the ammeter and
voltmeter, again taking in account the internal resistances. (8 marks)
5. (a) Explain the following terms as used in physics of semiconductors:
- Valence band
- Covalent bond
- Hole
- Recombination of carriers
- Acceptor impurity
- p-type semiconductor
- Drift of carriers
- Barrier potential
- Space charge in depletion region
- Biasing of a pn-junction (10 marks)
(b) Describe the principle of the following semiconductor devices give the electric symbol
and the main application of each
- Varactor
- LED
- Photodiode
- Zener photodiode (4 marks)
(c) A resistor ? 3.6? 1 R is connected in series with another ? 4.56? 2 R . What resistance
must be placed across 1 R so that the total resistance of the circuit is ? 6? T R (6 marks)
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Sph 2172: Physics Question Paper

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